Indeed, I ment that I only get the option to booth from HDD, the USB drive is not shown as an option to boot from. I run diskutil force unmount for each disk successfully but it still won't unmount the main disk. But it won't boot. 1. Says PID 0 prohibited (that's the kernal). I had it working but wanted to remove it all and try again. My Mac won’t turn on — now what? The older MacBooks & MacBook Pro’s didn’t offer USB boot support. NVRAM or PRAM (in older Mac computers) stores the information about system settings such as the startup disk to boot your Mac from, system date and time, screen resolution, etc. I'm having an issue all of the sudden with trying to restore Lion on my Air. 1. If you have bought an M1-based Mac or MacBook but need to upgrade your storage without buying a brand new device, you can set up your Mac to run from an external drive. As a result, booting from USB media is becoming the standard. Either way, here are the troubleshooting steps you should take to fix a Mac that won’t boot. Mac won't boot from USB drive: Prohibited sign. I plug it into the Thunderbolt-2 port on the Mac Mini, and the computer *does* see that partition, but it won't boot to it -- the computer simply turns itself off after about 5 seconds of trying to boot to that drive. I've been messing around with partitions and setting up triple boot (linx,windows,mac). And while users historically would pop a boot media disk into their DVD or CD drive, many computers no longer come with optical disk drives. M1 Macs can boot from any selected external drive with full security, which verifies the integrity of the operating system. I guess I'm out of luck. The first Mac was the MacBook Air which came out in January 2008. Again, after having waited 30 minutes the USB won't show up. Now when I boot, that SSD freezes up my BIOS. Question: Q: Macbook Air Won't Boot from USB Stick. 2. Installing macOS on a new HDD from USB drive stuck on grey screen with Stop sign. This may sound obvious, but check to see if your Mac has power or if its battery needs charging. I waited exactly 30 minutes and it still won't show up. 1. Here's how to boot … It does not prevent booting from external drives. Macbook keeps rebooting on installation USB after trying to reinstall - EFI partition empty. I take SSD out, try putting it in a USB hardrive tray reader, nothing. Or would you have more ideas I could try? I can't even get past the BIOS logo. The key thing to understand is that the machine won't just boot from any attached external drive. Specifically, the Lion thumb drive that I made a few months ago worked fine with an early 2008 MacBook Pro, but didn't show up in the boot picker on a mid-2007 MacBook (MacBook2,1) or a 2008 Mac … MacBook Pro, 15" (Early 2011), not booting. So I have reset the PRAM and SMC and tried again. 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